From c0829ec48ad86393859a10020099d0a17d850e11 Mon Sep 17 00:00:00 2001
From: Kwanghyo Park <kwanghyo.park@qt.io>
Date: Wed, 20 Aug 2025 11:59:43 +0300
Subject: [PATCH] Prevent improper fill for area series on the zero-axis
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When an area series had consecutive points on the y=0 axis,
the renderer would draw a horizontal line segment which caused
visual glitches when filled.

This change avoids filling that problematic segment on the y=0
axis, which fixes the improper fill.

Pick-to: 6.9 6.8
Fixes: QTBUG-139112
Change-Id: I4461cbf80af9b059ccfcc714234fed5039d0cd43
Reviewed-by: Tomi Korpipää <tomi.korpipaa@qt.io>
Reviewed-by: Jere Tuliniemi <jere.tuliniemi@qt.io>
(cherry picked from commit 52c5d1d3eca72e6a0cebd53d2df1c6070bc7a340)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/graphs2d/qsgrenderer/arearenderer.cpp | 34 +++++++++++++++--------
 1 file changed, 22 insertions(+), 12 deletions(-)

diff --git a/src/graphs2d/qsgrenderer/arearenderer.cpp b/src/graphs2d/qsgrenderer/arearenderer.cpp
index 624d5689..a62baa9b 100644
--- a/src/graphs2d/qsgrenderer/arearenderer.cpp
+++ b/src/graphs2d/qsgrenderer/arearenderer.cpp
@@ -168,21 +168,26 @@ void AreaRenderer::handlePolish(QAreaSeries *series)
     int extraPointCount = lower ? 0 : 3;
 
     if (series->isVisible()) {
+        qreal prevUpperY = 0;
         for (int i = 0, j = 0; i < upperPoints.size() + extraPointCount; ++i, ++j) {
             qreal x;
             qreal y;
-            if (i == upperPoints.size())
-                calculateRenderCoordinates(series,
-                                           upperPoints[upperPoints.size() - 1].x(),
-                                           0,
-                                           &x,
-                                           &y);
-            else if (i == upperPoints.size() + 1)
-                calculateRenderCoordinates(series, upperPoints[0].x(), 0, &x, &y);
-            else if (i == upperPoints.size() + 2)
-                calculateRenderCoordinates(series, upperPoints[0].x(), upperPoints[0].y(), &x, &y);
-            else
-                calculateRenderCoordinates(series, upperPoints[i].x(), upperPoints[i].y(), &x, &y);
+            qreal upperX;
+            qreal upperY;
+            if (i == upperPoints.size()) {
+                upperX = upperPoints[upperPoints.size() - 1].x();
+                upperY = 0;
+            } else if (i == upperPoints.size() + 1) {
+                upperX = upperPoints[0].x();
+                upperY = 0;
+            } else if (i == upperPoints.size() + 2) {
+                upperX = upperPoints[0].x();
+                upperY = upperPoints[0].y();
+            } else {
+                upperX = upperPoints[i].x();
+                upperY = upperPoints[i].y();
+            }
+            calculateRenderCoordinates(series, upperX, upperY, &x, &y);
 
             if (i == 0) {
                 painterPath.moveTo(x, y);
@@ -205,8 +210,13 @@ void AreaRenderer::handlePolish(QAreaSeries *series)
                     ++j;
                 } else {
                     painterPath.lineTo(x, y);
+                    if (i != 0 && i < upper->points().size()
+                    && upperY == 0 && prevUpperY == 0) {
+                        painterPath.moveTo(x, y);
+                    }
                 }
             }
+            prevUpperY = upperY;
         }
     }